In this study, the impact of cage culture of rainbow trout (Oncorhynchus mykiss Walbaum), on benthic communities using biological indicators located along the coastal areas of the South Caspian Sea (Nashtarudregion, Mazandaran Province, Iran) was investigated. Monthly samplings from 4 stations were carried out from January 2016 to May 2016.The physical and chemical characteristics of water were measured on a monthly basis. Sediment samples were taken using Ekman Grab. The ecological indicators such as Shannon–Wiener index of diversity, H, Simpson, S, and Margalef, R, was routinely used. The biomass-dominant faunal groups were Bivalve (146.16 g/m2 (,Crustacea (24.5 g/m2) and Polychaeta (10.5 g/m2).The greatest variety of benthos was found under the cage and the lowest range was found150-300 m around the cage that was significantly difference (P<0.05). Results of current study showed that, the percentage of sand was greater than that of silt and clay throughout the experimental period. Sediment organic matter (OM%) reached extremely high concentrations beneath the control (P<0.05), when compared surrounding area. A positive correlation coefficient was found betweenthe Shannon–Wiener diversity index (H'), and biomass of benthic organisms (p=0.001; r= 0.684). According to results of species diversity, and amount of organic matter in the cage area, indicated that specific richness levels were in bad ecological statues.